One type of sender that is used in motor vehicles comprises a resistor card that is disposed in a fuel tank in a manner that exposes it to whatever fuel is used by the vehicle (gasoline and/or alcohol for example), including fuel additives, sour gas, and/or contaminants. The sender is operated by a float that follows the level of liquid fuel in the tank. As the float assumes different levels within the tank, its motion is transmitted by a float rod, or arm, to a contact arm, causing a contact on the arm to move along a succession of commutator bars extending from locations along the length of a resistor track printed on a resistor card, thereby selecting a portion of the resistor in correlation with the level of the float. The selected portion provides a variable resistance that is electrically connected with instrumentation that operates a fuel gauge that can be observed by the driver. The float rod is mounted for pivotal movement via a bearing, and the float is disposed at an end of the rod opposite the bearing. As the float moves, the rod imparts pivotal motion to the contact arm, causing its contact to move in an arc along the succession of commutator bars, changing the value of the variable resistance as it moves. In that design for a resistive type fuel level sender, the commutator bar contact produces a result similar to a contact moving in an arc along a potentiometer or variable resistor track, changing the value of the variable resistance as it moves.
The force that the contact is able to apply against the resistor on the resistor card is important in enabling the sensor to provide a service life that will meet relevant specifications. Over the life of a sender the force that the contact exerts on the resistor may vary for one or more different reasons, such as fuel slosh in the tank and/or looseness in the bearing. The use of a silver palladium alloy as the resistor commutator may reduce the effects of those factors. Nonetheless the contact may at times lose contact with the resistor, creating a momentary open circuit. Events that may cause such open circuits include intrusion of foreign particles between the contact and the resistor, corrosion of the commutator, oxidized fuel coating, and high-G loads experienced by the sender. Momentary open circuits create excess wear on the contact and the resistor commutator.
A sender that precludes those undesirable possibilities and that meets certain cost objectives is therefore seen to be a desirable improvement.
The durability and accuracy of a fuel sender are also important, especially where a motor vehicle manufacturer warrants a fuel system and/or its components either for legal compliance and/or by competitive considerations. Failure to meet relevant compliance criteria can expose a motor vehicle manufacturer to costly penalties and/or warranty claims.
Accordingly, it is believed that a sender that provides both increased durability and accuracy over an extended period would be a significant improvement in the state of the art.
U.S. Pat. Nos. 3,739,641 and 4,987,400 describe gauges having magnetically driven senders in which the contacts are housed within sealed enclosures. The gauge of U.S. Pat. No. 3,739,641 is sealed against intrusion of volatile vapors that may accumulate from many sources and might ignite from a spark. An example given is in the bilge of a marine vessel. The gauge of U.S. Pat. No. 4,987,400 is said to be ultrasonically sealed for withstanding at least eight inches of mercury pressure differential. Both patents teach the use of an external magnet driving a magnet internal to the enclosure where the magnet is rotated by a coupling to a float. The enclosure materials are not selected to be highly impermeable to fuel or fuel vapors, only sufficient to prevent spark ignition.
Considerations in the prevailing design of motor vehicle fuel systems either tacitly or explicitly mandate that the fuel sender be contained within the fuel tank where it may at times be immersed in liquid fuel. A contact-containing enclosure that is external to a tank, as in U.S. Pat. Nos. 3,739,641 and 4,987,400, is not seen to be suitable for placement in a fuel tank of a motor vehicle where it must withstand immersion in a hostile liquid fuel that can at some times be quite hot and at others, quite cold, and that may contain various contaminants, additives, foreign substances, etc.
Accordingly, it is believed that an in-tank fuel sender for a motor vehicle that maintains its accuracy when exposed to liquid fuels, especially liquid fuels like gasoline, over an extended period would be another significant improvement in the state of the art.
Prevailing fuel system design practices in the automotive industry employ a fuel pump module that is assembled into a fuel tank, typically through an opening in a top wall of the tank that is subsequently closed. A fuel sender is typically part of the fuel pump module. Certain of the known systems comprise a fixed mounting of the sender in an assembly that is installed in a tank. The assembly has a construction that forces its lower end against a bottom wall of the tank thereby bodily positioning the sender within the tank relative to the bottom wall.
Accordingly, an in-tank fuel sender that can be conveniently assembled into fuel pump modules is also seen desirable.